Pump with separate pumping stages for pumping a plurality of liquids

ABSTRACT

The pump comprises three distinct series of pumping stages driven on a single shaft by the same motor. Between the first and second series of pumping stages, the liquid is diverted from the pump through a by-pass towards, for example, a filtering device for removing the liquid as many impurities as possible. Then, the filtered liquid is conveyed back to the second series of pumping stages of the pump where the liquid is pumped at high pressure before being conveyed through a by-pass outside of the pump and towards a treatment chamber, such as a chamber for reverse osmosis, nanofiltration, or the like. The permeate (filtered solution) is removed from the installation whereas the solute (concentrated solution) is, in large part, reconveyed towards a third series of pumping stages, at the discharge of which the liquid is mixed with the filtered liquid from the second series of stages and the mixture is then conveyed again towards the treatment chamber. This high yield system eliminates a second and third pump. The pump can also be used for pumping independently, that is without mixing, more than one liquid. In this case, the pumping stages are once again separated from one another, with each stage pumping its respective liquid. The stages are capable of pumping liquids with different rates and at different discharge pressures.

FIELD OF THE INVENTION

The present invention relates to a pressure and liquid recirculationpump which includes mainly an intermediary inlet and an intermediaryoutlet for the liquid being pumped. More particularly, the presentinvention relates to an installation used for the concentration of asolution, such as maple water, impure water, and others, by way of aprocess using a semi-permeable membrane.

According to the present invention, the pressure pump is used both forfeeding the liquid, such as maple water, from a stocking tank towards afilter, and then for the introduction under pressure of the filteredliquid in a housing which encloses the membrane, and finally forrecirculating the liquid so as to remedy to the filling in or pluggingof the membrane and to reduce the concentration at the membrane surface,thereby resulting in a lowering of the osmotic pressure and producing anincrease in the permeation flow.

DESCRIPTION OF THE PRIOR ART

It is well known in reverse osmosis processes that the solutions of saltor other solutes, notably those having low molecular weights, forexample sea water, maple water and others, are introduced to a selectivemembrane and submitted to a pressure. Contrary to what happens in thecase of a normal osmosis where there is an equilibrium of the solutionon both sides of the membrane, the reverse osmosis results in that asolution having a low, and even extremely low, concentration appears onthe side of the membrane opposite that of the original solution. Insummary, in order to reverse the normal osmotic flow from the side ofthe membrane where the solution is less concentrated towards the sidewhere the solution is more concentrated, there is exerted on thesolution to be treated a pressure differential higher than the osmoticpressure differential of the solutions in contact with the surfaces ofthe membrane.

It has now been noticed that, during a reverse osmosis process, theconcentration at the interface membrane-solution to be treated is higherthan the average concentration on the high pressure side of themembrane. This abnormally high concentration at the interface penalizesthe quality of the product obtained by the reverse osmosis processbecause, on the one hand, a considerable amount of salt or other mattersin solution, in contact with the membrane is rejected, and on the otherhand, by recirculation, there is a reduction of the concentration at thesurface of the membrane of the not-very-soluble components which can betolerated without precipitating on the membrane.

Commonly, the expression filling-in or plugging refers to all phenomena,other than temperature and compaction variations, which reduce amembrane's permeability to pure water. The phenomena are linked to thepresence of solutes or of matters in suspension, notably colloids,bacteria, etc., which can deposit at the surface or in the pores of themembrane. The plugging can be more or less rapid depending on the natureof the particles which are present and on their concentration at thesurface of the membrane. To obviate to the problems resulting from theplugging of the membrane, which is more or less reversible, rinsing ofthe membrane using hot or cold water or the cleaning thereof are carriedout.

In the production or maple syrup, the maple water has always beenevaporated until the syrup was obtained. Now, with the high increase inthe price of energy, it is useful to proceed with the evaporation fromthe solution which is more concentrated than the water directly obtainedfrom the maple tree. In order to do so, reverse osmosis processes havebeen used, wherein the substantially pure water is discharged and theconcentrated water retained. As in the other reverse osmosis cases,there is a serious problem of plugging at the level of the membrane.Indeed, the solutes contained in the maple water are essentially sugarsand minerals. The maple water also contains some bacteria, the number ofwhich varying from a few dozens to many millions per ml. The solutes arealmost all retained by the membranes of the reverse osmosis ornanofiltration types, notably almost 100% for the sugars and more than95% for the minerals. A fortiori, the particles in suspension, includingthe bacteria, are also retained. The sugar molecules, which, beinglarger, circulate less rapidly than the ions, represent most of theminerals in the solution. All of this favors, relatively, a largeraccumulation of sucrose than of minerals at the surface of the membrane,which results in a considerable plugging of the latter.

Nowadays, it has been observed that the best way of overcoming, at leastpartly, the problem of the plugging of the membrane resides in therecirculation of the liquid being treated, by reverse osmosis. To do so,the liquid can be recirculated in the same pump, or the recirculationcan be achieved by way of an additional pump. In a system withoutrecirculation, there has been obtained a recovery of 19% (permeateflow:feed flow), and consequently, there is a large waste of water. If,on the other hand, recirculation takes place in the same pump, anaverage recovery of approximately 24% is obtained; but there is also alarge waste of water and energy. To obtain a satisfactory yield, theremust be used three similar systems, one after the other, which is veryexpensive. To obtain a adequate output of approximately 75%, in a soleoperation, two pumps can be used wherein one of the pumps is used onlyfor recirculation. This alternative is, however, very expensive becauseof the presence of two pumps.

Moreover, a further pump is required to supply the untreated maple waterstocked in a tank (or in any reservoir) from this tank towards a filterwhich will eliminate some of the impurities found in the untreated maplewater. Therefore, a first pump is normally used for supplying theuntreated maple water from the stocking tank towards the filter, with asecond pump being used for supplying the filtered maple water from thefilter to the reverse osmosis device, and finally with a third pumpbeing used for recirculating the concentrated solution removed from thereverse osmosis device towards the inlet of this same device.

It would thus be useful to use a system having a single pump and havinga recovery substantially improved with respect to what is presentlyknown and which would be comparable to the use of three pumps.

Regarding the prior art, the following documents must be noted, althoughirrelevant with regard to the present invention:

U.S. Pat. No. 3,472,765

U.S. Pat. No. 3,505,215

U.S. Pat. No. 4,705,625

U.S. Pat. No. 4,773,991.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a novelpump adapted for certain uses that normally require at least twoconventional pumps and characterized in that the pump comprises at leasttwo distinct pumping means adapted to pump at least two liquids andespecially comprises a liquid intermediary outlet and a liquidintermediary inlet.

Another object of the present invention resides in a pump comprising atleast two distinct series of pumping stages and separation meansdisposed between the liquid derivation intermediary outlet andintermediary inlet.

Another object of the present invention resides in that, at the end ofthe first series of pumping stages, the liquid is completely removedfrom the pump by way of the intermediary outlet and in that a liquid,sometimes the same, but further treated in one form or another, reachesthe second series of pumping stage by the intermediary inlet.

Therefore, in accordance with the present invention, there is provided apump comprising a housing and at least first and second pumping means inthe housing which are adapted to be driven by a single motor, the firstand second pumping means including respectively a liquid inlet and aliquid outlet and being separated in the housing by separation means;the first and second pumping means include also, respectively, a liquidintermediary by-pass outlet and a liquid intermediary by-pass inletdisposed on one side and the other of the separation means such that aliquid reaching the housing by the inlet is pumped by the first pumpingmeans and leaves the housing through the intermediary by-pass exit, aliquid thus being capable of also reaching the housing by theintermediary by-pass inlet and being pumped by the second pumping meansup to the outlet.

Also, in accordance with the present invention, there is provided a pumpcomprising a housing and at least a first and second pumping meansinside the housing which are adapted to be driven by a single motor, thefirst and second pumping means each comprising a liquid inlet and aliquid outlet and being separated in the housing by separation means,the first and second pumping means being thus adapted for pumpingdifferent liquids without any mixture thereof in the pump, the liquidsreaching the pumping means by respective inlets and leaving the same byrespective outlets.

Further in accordance with the present invention, there is provided aninstallation for the concentration of a solution by reverse osmosis orother process using a semi-permeable membrane, this installationcomprising a housing enclosing a semi-permeable membrane responsible forthe concentration of the solution; a pump allowing for the introductionof the solution under pressure in the housing, as well as means forensuring the recirculation of part of the solution. The pump comprisesfirst and second pumping means, such as two series of pumping stages,adapted to be driven by a single motor, the first and second pumpingmeans being hydraulically separated in the pump by separation means, thefirst pumping means including an inlet and an outlet for the untreatedliquid, the second pumping means including an inlet and an outlet forthe recirculated liquid such that a liquid reaching the pump through theinlet for untreated liquid is pumped by the first pumping means and isremoved from the pump through the outlet for the untreated liquid,whereas a concentrated liquid from the housing reaches the secondpumping means through the inlet for the recirculated liquid and isremoved from the pump through the outlet for the recirculated liquid,the liquid and the recirculated liquid being mixed together downstreamof the first and second pumping means and upstream of an inlet of thehousing.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus generally described the nature of the invention, referencewill now be made to the accompanying drawings, showing by way ofillustration preferred embodiments thereof, and in which:

FIG. 1 is a schematic representation of a pump in accordance with thepresent invention having derivation intermediary inlets and outlets andinstalled on a liquid filtration and filtered liquid concentrationreverse osmosis system;

FIG. 2 is a fragmented elevational view, partly in longitudinalcross-section, of the pump of FIG. 1;

FIG. 3 is a developed and enlarged view of the section of the pump whichis framed by the dotted lines on FIG. 2; and

FIG. 4 is a schematic and fragmented representation of a pump havingmultiple inlets and outlets also in accordance with the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the drawings, and more particularly to FIG. 1, it isseen that the illustrated installation comprises a pump P in accordancewith the present invention connected to a source of liquid (notillustrated), such as a stocking tank, by a conduit 10 connected to aprimary inlet 12 of the pump P and to a housing 14 comprising asemi-permeable membrane 16 by a main outlet 18 and a conduit 10. Asubmersible or exterior motor M (or M' see FIG. 4) is evidently foreseenin the body of the pump P or at the exterior of the pump which isessentially constituted by a first series of pumping stages 22, of asecond series of pumping stages 24 and a third series of pumping stages26 successively disposed in an aligned manner in the housing 14 of thepump P so as to be driven by a single shaft connected to motor M, M'inside a cylindrical housing 27.

On the other hand, the housing 14, including membrane 16, is connectedonce again to the pump P by a conduit 28 which is connected at thebeginning of the third series of pumping stages 26 by means of asecondary inlet 20.

It is to be noted that the components constituting the first and secondseries of pumping stages 22 and 24 are so selected as to ensure theconveying under pressure of a volume of a solution to be concentratedwhich corresponds generally to the permeation capacity of the membrane16 in the installation and to an equivalent evacuation of approximately10% to 25% of the permeation rate. The permeate (i.e. water practicallypure) is directed outside the housing 14 (and withdrawn from theinstallation) by a conduit 48 whereas a concentrated solution (i.e.maple water concentrated in sugar) is rejected from the recirculation byan evacuation conduit 50. These constitutive elements have beenillustrated by reference numeral 32.

Concerning the constitutive elements of the third series of pumpingstages 26, they should deliver an important volume of recirculationliquid. The constitutive elements of the third series of stages 26 arerepresented by reference numeral 34. Finally, at the level of thesecondary inlet 30 in the pump P between the second and third series ofpumping stages 24 and 26, elements 52 have been foreseen and constitutea guide enabling the simultaneous conveying towards the third series ofstages 26 of the liquid to be concentrated coming from the first andsecond series of pumping stages 22 and 24 as well as of the recirculatedliquid in the third series of pumping stages 26 of the pump P, viaconduit 28 and secondary inlet 30, from the housing 14 where membrane 16is located.

The present invention is characterized by the structure which isinserted between the first and second series of pumping stages 22 and 24and between the second and third series of pumping stages 24 and 26.Indeed, as described in detail hereinafter, the liquid from the stockingtank by means of the conduit 10 and the primary inlet 12 cannot accessdirectly, from the first series of stages 22, the second series ofpumping stages 24 through the housing 27 of the pump P since thereexists, in the latter, between the first and second series of pumpingstages 22 and 24 and between the second and third series of pumpingstages 24 and 26, devices for the total interruption of the flow ofliquid in the pump P. Therefore, with reference to FIG. 1, the end ofthe first series of pumping stages 22 is equipped with a firstintermediary outlet 38 which opens onto the first derivation conduit 40.The liquid deviated outside the pump P is conveyed by this firstderivation conduit 40 towards, for example, a filter F (for example, 5microns) conceived to withdraw some of the impurities in the liquid,such as maple water. The filtrated liquid is then conveyed by means of asecond derivation conduit 42 towards an intermediate inlet 44 whichcommunicates with the beginning of the second series of stages 24.

Similarly, the liquid thus filtrated is conveyed at high pressure by thesecond series of pumping stages 24 and the liquid at high pressure isforced to exit the pump P by a second intermediate outlet 45 andconnects, through a conduit 47, with conduit 20 where the filtratedliquid at high pressure is mixed to the recirculated liquid which isdelivered by the third series of stages 26 through the main outlet 18.

For more detailed descriptions of elements 32 and 34, one can refer to aco-pending Canadian application No. 2,059,392 filed Jan. 15, 1992wherein the elements 32 and 34 are impellers, those situated at thelevel of the first and second series 22 and 24 of the pumping stagesbeing adapted to ensure the conveying of a given volume of liquid to beconcentrated towards the housing 14, which volume is dictated by thecapacity of the membrane 16. Concerning the third series of pumpingstages 26, they consist of impellers having a greater volume than thoseforeseen for stages 22 and 24 since they must carry out the conveying ofthe recirculated liquid towards the membrane 16. It is to be noted thatthe three series of stages 22, 24 and 26 are all driven by a commonshaft 46 (which is itself driven by a single motor, i.e. motor M) havinga hexagonal section. Generally shaft 46 drives in rotation the impellersof elements 32 and 34 whereas the diffusers and the housings, orperipheral rings of the latter, remain fixed with respect to the shaft46.

Between the first and second series of pumping stages 22 and 24 andbetween the second and third series of pumping stages 24 and 26 arelocated derivation elements 52. These derivation elements 52 situatedbetween the first and second series of stages 22 and 24 are illustratedin detail in FIGS. 2 and 3. The derivation elements 52 situated betweenthe second and third series of pumping stages 24 and 26 being similarare therefore not illustrated in detail. Each derivation element 52includes a peripheral rim 54 which can be hermetically fitted with anadjacent rim 54 or with elements 32 of the first and second series ofpumping stages 22 and 24. The rim 54 is connected at a central hub 56having a drilled hole by means of grooves 58 having a radial orientationand in the form of blades. The rim 54, the central hub 56 and thegrooves 58 are integrally made of a plastics construction. A bronzebearing 60 fixed in the hole of the central hub 56 receives internally asleeve 62 which displays an inner opening having a shape correspondingto that of shaft 46 such that the sleeves 62 are rotably displaced withthe shaft 46 inside the fixed bearing 60.

The intermediate outlet and inlet 38 and 44 communicate with hollowparts of the derivations elements 52 (i.e., those parts provided betweenthe grooves 58 in a longitudinal fashion and between the central hub 56and the rim 54 in a radial fashion) by means of openings conventionallyprovided (for example, as in the patent application mentioned above) inthe rims 54. A separation disc 64 located in a fixed manner between twoof the elements 52 and also located between the intermediate outlet andinlet 38 and 40 is provided to by-pass all the liquid outside the pump Pby the intermediate outlet 38, towards the filter F by the derivationconduit 40, the filtrated liquid arriving once again at the pump P atthe level of the second series of stages 24, by the intermediary inlet44. The separation disc 64 is full, except for an inner opening intendedto encircle the sleeves 62. To this opening, the disc comprises aflexible annular section 66, preferably covered with Teflon™, whichbears against the sleeve 62 in order to ensure a sealing engagementinside the pump P longitudinally on either side of the separation disc64 at the level of the interfaces between the fixed pieces and rotatingpieces. The flexible annular section 66 comprises two legs 67 so as toprovide a bidirectional seal joint. The tightness between the peripheryof the rims 54 and the interior of the housing 27 of the pump P isensured by toroidal joints 68.

The derivation elements 52 of the second and third series of pumpingstages 24 and 26 and, more particularly the separation disc 64, causethe by-passing of the filtered liquid outside the pump P by a secondintermediary outlet 45 and towards the housing 14 by means of conduits47 and 20.

Also, as an example, the liquid conveyed to the primary inlet 12 mayflow under a 10 gallons per minute (GPM) and at a pressure of 30 psi.The liquid under a flow rate of 10 gallons per minute flows in thederivation conduits 40 and 42, respectively, under pressures, forexample, of 70 psi and 55 psi, the difference being due to the pressureloss in the filter F. The liquid coming out of the first and secondseries of pumping stages 22 and 24 has a pressure of 485 psi and avolume of 10 gallons per minute. The recirculated liquid arriving byconduit 28 and the secondary inlet 30 to a third series of stages 26 hasa pressure of 485 psi and a discharge rate of 60 gallons per minute. Theliquid coming out of the third series of pumping stages 26 has thereforea rate of 60 gallons per minute and a pressure of 500 psi since thesecond series of stages is provided to pump a high volume whilepartially increasing the pressure of the liquid arriving. Therefore, 70GPM of liquid at 500 psi are mixed outside the pump P and are directedby the conduit 20 towards the housing 14 which comprises thesemi-permeable membrane 16. The permeate coming out of the housing 14 bythe outlet 48 can have a rate of 7.5 GPM at a pressure which is almostnil. Consequently, 62.5 GPM are directed towards the recirculationconduit 28 and the outlet of the concentrated liquid 50. For example,the discharge by outlet 50 can be of 2.5 GPM at a pressure which isnearly nil whereas the recirculated liquid through the conduit 28 canhave a discharge rate of 60 GPM at a pressure of 485 psi. Therefore, thefirst and second series of pumping stages 22 and 24 increases thepressure of the inlet liquid whereas the third series of pumping stages24 pump a considerable recirculation liquid volume. The assembly of thethree series of pumping stages enables the pumping at high pressure ofan important volume of liquid with derivation and recirculation, andthis, with a single pump instead of three.

It is to be noted that one can use this installation not only for theconcentration of maple water, but also for all other liquids to beconcentrated such as sea water, etc. One can also use this pump havingthree series of stages in a manner that it would not be associated witha reverse osmosis operation. All systems using a liquid under pressureand which necessitates a derivation, and perhaps a recirculation of thelatter, could evidently use the pump of the present invention resultingin the dispensing of using a second and a third pump.

The present pump enables unlimited pumping at the level of flow ratesand pressures.

Referring now to FIG. 4, another pump P' also made in accordance withthe present invention is driven by an exterior motor M' by means of ashaft, such as the hexagonal shaft 46 of FIGS. 1 to 3. The pump P' ofFIG. 4 is provided to pump four different liquids without having amixture therebetween. The four liquids are pumped from tanks 100, 102,104 and 106 by the first, second, third and fourth series of pumpingstages 108, 110, 112, and 114, respectively.

The four series of pumping stages comprise liquid inlets 116, 118, 120and 122, respectively, and liquid outlets 124, 126, 128 and 130,respectively. The conduits for conveying these liquids from reservoirs100, 102, 104 and 106 to the inlets 116, 118, 120 and 122 of the pump P'are all identified by reference 132 in FIG. 4 whereas the four liquidoutlet conduits are identified by reference 134.

The series of pumping stages 108, 110, 112 and 114 are separated fromone another in the housing 27 of the pump P' by derivation elements 52identical to those of FIGS. 1 to 3. In FIG. 4 one can easily see thatthree separation discs 64 are used to separate the different series ofpumping stages.

Therefore, the liquid contained in the reservoir 100 will be pumped bythe first series of pumping stages 108 of the pump P' and this, fromleft to right in FIG. 4 and in the direction of disc 64 separating thefirst and second series of pumping stages 108 and 110. The liquid comingfrom the reservoir 102 will flow from right to left in the second seriesof stages 110 of pump P' and in the direction of the first series ofpumping stages 108. The liquids of reservoir 104 and 106 will flowrespectively in the third and fourth series of pumping stages 112 and114 from left to right in FIG. 4. Therefore, in the present pump P', theliquids can circulate independently from left to right or from right toleft in the different series of pumping stages 108, 110, 112 and 114.Equally, the flow rates and pressure of the liquids can vary from oneseries of pumping stages to another.

The pump P' therefore enables the pumping of many liquids havingdifferent flow rates and different pressures with the assistance of asingle motor which is coupled to a single shaft adapted to drive thedifferent stages of pumping, each one being associated to a respectiveliquid.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. Installation for theconcentration of a solution by reverse osmosis or other process using asemi-permeable membrane, said installation comprising a housingenclosing a semi-permeable membrane responsible for the concentration ofsaid solution; a multistage centrifugal pump allowing for theintroduction of said solution under pressure in said housing; as well asmeans for ensuring the recirculation of part of said solution,characterized in that said centrifugal pump comprises first and secondpumping means adapted to be driven by a single motor, said first pumpingmeans consisting of a first series of pumping stages for untreatedliquid; said second pumping means consisting of a second series ofpumping stages for recirculated liquid; said first and second pumpingstages being hydraulically separated in said centrifugal pump byseparation means, said first pumping means including an inlet and outletfor the untreated liquid, said second pumping means including an inletand an outlet for the recirculated liquid such that a liquid reachingsaid centrifugal pump through said inlet for untreated liquid is pumpedby said first pumping stages and is removed from said pump through saidoutlet for the untreated liquid, whereas a concentrated liquid from saidhousing reaches said second pumping stages through said inlet for therecirculated liquid and is removed from said centrifugal pump throughsaid outlet for the recirculated liquid, the liquid and the recirculatedliquid being mixed together downstream of said first and second pumpingmeans and upstream of an inlet of said housing.
 2. Installation asdefined in claim 1, wherein said housing is cylinder-shaped, whereinsaid separation means comprise a solid disc hermetically andtransversally mounted between said housing and a shaft depending from adriving motor while allowing for the rotation of said shaft which drivessaid first and second pumping means, in such a way that said discprevents the liquid pumped by said first pumping means from directlyreaching said second pumping means, thereby forcing the liquid outsideof said housing and thus of said pump through said outlet for theuntreated liquid.
 3. Installation as defined in claim 1, wherein liquidderivation means are provided for said first pumping means such that theuntreated liquid having reached said inlet of said first pumping meansis removed from said first pumping means through an intermediary outletand is returned thereto through an intermediary inlet, whereby theuntreated liquid can be treated outside of said housing and between saidintermediary outlet and inlet.
 4. Installation as defined in claim 3,said liquid derivation means consist of filtering and piping meansconnected to said intermediary outlet and inlet outside of said housing,whereby the untreated liquid may be filtered outside of side housing andbetween said intermediary outlet and inlet.